In the metal casting industry molten metal is cast into molds containing sand cores made from foundry sand and binders. These sand cores are conventionally bonded with organic resins which, during curing and during casting of the metal, decompose and evolve byproducts which are odoriferous, offensive fumes which are not only skin irritants but in most cases toxic. The molds themselves are made from foundry sand bonded with oils, clays and/or organic resins. Thus, during their use, similar problems can occur.
A great percentage of the sand binders used by the foundry industry are made of phenol- and urea-formaldehyde resins, phenolic- and oil-isocyanate resins, and furan resins. Almost all these binders and their decomposition products such as ketones, aldehydes and ammonia are toxic. The principal effect on man is dermatitis which occurs not so much from completely polymerized resins, but rather from the excess of free phenol, free formaldehyde, alcohol or hexamethylenetramine used as a catalyst. Formaldehyde has an irritating effect on the eyes, mucous membrane and skin. It has a pungent and suffocating odor and numerous cases of dermatitis have been reported among workers handling it. Phenol is a well-known poison and is not only a skin irritant but is a local anesthetic as well, so that burns may not be felt until serious damage has been done. Besides being capable of causing dermatitis it can do organic damage to the body. Furfuryl alcohol defats the skin and contact with it has to be avoided. Hexamethylenetetramine is a primary skin irritant which can cause dermatitis by direct action on the skin at the site of contact. Urea decomposes to carbon dioxide and ammonia, the latter of which is intolerable in toxic concentrations. In addition to the binders, some processes use flammable gases such as triethylamine as a curing agent. Capturing or destroying gases, smoke and objectionable odors are only temporary, stop-gap expensive solutions. New binders are needed that completely eliminate the sources of offensive odors and toxic gases.
Many of the organic binders are hot setting and therefore require heating to cure. Hot molds not only add hazards and complicate pollution control problems but add economical problems related to increased use of energy and increased equipment, maintenance and operation costs.
An alternative is to use inorganic cold setting binders, such as sodium silicate, which set at room temperature without producing objectionable gases or vapors. The use of silicates, however, results in the silicate bond remaining too strong after casting, so that the core is still coherent, and has to be removed by use of violent mechanical agitation or by dissolving the silicate bond with a strong, hot aqueous alkali. The problem may be lessened to a degree by using sodium silicate solutions admixed with organic materials such as sugar, but even in this case the core is still coherent after casting and requires extreme measures for removal such as violent mechanical agitation.
Thus, there is a need to create a binder for sand in making cores and molds for casting metals such as aluminum, bronze, or iron, that will have satisfactory high strength before the metal is cast, retain sufficient hot strength and dimensional stability during the hot metal pouring, but which will have strength after the metal has been cast and cooled, that the sand can be readily shaken out of the cavities formed by the cores; the binder also should be one that will not evolve unreasonable amounts of objectionable fumes when the sand cores and molds are subjected to molten metal.